1. The problem statement, all variables and given/known data see link for a picture of the situation, http://i50.tinypic.com/n5g3z5.jpg 2. Relevant equations (1/2)mv^(2) , (1/2)k*l^(2) 3. The attempt at a solution Total energy of the system at the given point of time is mv^(2)/2+kl^(2)/2 = 0.6*100/2+100*0.25/2 = 30+12.5 = 42.5 J At the maximum and minimum values of l, v = 0 => kl2/2 = 42.5 => l = √(85/k) => l = ±0.922 m maximum l = 0.922m and minimum l = -0.922m Not terribly confident in this approach however, any guidance would be appreciated. Thanks!